新疆东准噶尔地区早泥盆世软舌螺的发现及其古生态和古地理意义OA北大核心CSTPCD

The newly discovered hyoliths yielded from the Lower Devonian of East Junggar of Xin-jiang,China,are documented herein for the first time,including three genera and three species:Fuyunotheca wangi gen.et sp.nov.,Costulatotheca schleigeri Earp,2019,and Ottomarites sp.As a new genus and species,F.wangi gen.et sp.nov.is mainly distinguished by typically oblate oval to subtriangu-lar cross-section,swollen dorsal side with a pronounced median ridge,ventral side weakly convex.Sur-face sculpture prominent transverse striations and weakly longitudinal streaks on both dorsum and venter,and several sets of remarkable ribs parallel to the aperture in the anterior third of the conch.Palaeoecologi-cal analysis shows that F.wangi gen.et sp.nov.is a kind of orthothecids,which could live in a normal,oxygenated shallow-marine environment with certain degree of hydrodynamics.Furthermore,based on the Devonian hyoliths reported so far from all over the world,it has been recognized 14 genera and 66 species as valid from 12 areas in 11 countries(excluding indeterminate genera and species).Palaeogeographic distribution analysis shows that the Devonian hyoliths were mainly distributed in the southern hemisphere,that were positioned near the Laurussia and Gondwana,with a few species sporadically distributed in other plates or blocks.Newly discovered specimens of these early Devonian hyoliths not only expands the palaeo-geographic distribution range of hyoliths during the Devonian period,but also provides new evidence for inter-continental biostratigraphic correlation. Phylum uncertain Class Hyolitha Marek,1963 Order Orthothecida Marek,1966 Family INDET. Fuyunotheca gen.nov. Type species Fuyunotheca wangi gen.et sp.nov. Etymology Fuyun(Gr.)is derived from the Chinese Pinyin of the word"Fuyun"of Fuyun Coun-ty,Altay Prefecture,Xinjiang.The theca(Gr.)means the capsule,membrane,sheath,and shell of organisms. Diagnosis Orthothecids having straight and middle-sized conch with oblate oval to subtriangular cross-section;swollen dorsal side with a pronounced median ridge;ventral side flat to weakly convex.Aperture straight or almost straight.Apical part of shell blunt.No apical septa were found.Surface sculp-ture prominent transverse striations and weakly longitudinal streaks on both dorsum and venter,and se-veral sets of remarkable ribs parallel to the aperture in anterior third of the conch near the apertural side.The separation distances between each set of transverse ribs gradually widen from the aperture to the apical end of the shell.Operculum is unknown. Remarks The main difference between Hyolithida and Orthothecida is that the former has protru-sions(lips)on the ventral side of aperture(Malinky and Racheboeuf,2010).The aperture of the new genus Fuyunotheca gen.nov.is straight and without protrusions,so it can be attributed to the order Or-thothecida Marek,1966.According to the taxonomy of Orthothecidae Sysoev,1958 revised by Malinky(2009b),its venter is concave to flat,and sculpture of conch consists of longitudinal ridges or lines,without transverse ornamentation.The new genus has the similar conch with that of the family Orthotheci-dae,but differs from them in having a flat to slightly convex venter and sets of unique transverse ribs on the conch.The new genus is similar to Bolitheca Marek and Isaacson,1992 and Neobactrotheca Marek and Isaacson,1992 from the Middle Devonian Icla Formation of Bolivia.However,specimens of Bolitheca ex-hibit pronounced longitudinal ridges on the dorsum,the semi-elliptical cross-section,and rounded lateral ridges(Malinky and Racheboeuf,2011).Specimens of Neobactrotheca have many longitudinal ridges and no median ridges on the dorsum.Besides,the conch of Neobactrotheca differs from that of this new species by having elliptical cross-section and smooth transitions to the lateral ridges(Marek and Isaacson,1992).It is for this reason that we establish a new genus,belonging to the indeterminate family. Fuyunotheca wangi gen.et sp.nov. Fig.2 Etymology The species is named in honor of Wang Hongzhen,the famous paleontologist who de-scribed hyoliths from China for the first time. Holotypoe One well-preserved dorsum of conch,specimen number:XJLD-001(Fig.2-A). Paratype One well-preserved venter of conch,specimen number:XJLD-003(Fig.2-C). Other materials Specimen registration number:XJLD-002,004-046.Venter or dorsum of 44 conchs with incomplete aperture or initial part. Diagnosis As for the genus. Description The conch is straight and conical,expanding gradually and evenly from the apex to the aperture,and the aperture is thickened(Fig.2-E,ta).The growth angle of the conch is about 9.90°.The length of the shell is about 41 mm,and the diameter of the aperture is about 9 mm.The dorsum passes through the oblate lateral ridge to the venter,and its cross-section has oblate oval to subtriangular shape(Fig.2-B2).There is a median ridge running through the conch(Fig.2-A,B1,dmr)in the middle of dorsum.There are slightly inclined surfaces on both sides of the ridge,and a longitudinal groove on the right slope(Fig.2-A,gr).Sets of remarkable ribs(Fig.2-A,2-C,2-D,tr)parallel to the aperture are distributed in the anterior third of the conch.There are five groups of ridges(Fig.2-A,tr1-trs)which are made up of 2-5 transverse ridges in each group.The separation distances between each set of transverse ribs gradually widen from the aperture to the apical end of the shell.Surface of shell from the middle to the initial part covered with slight growth lines(Fig.2-F,tl).In addition,the conch is also decorated with weakly longitudinal lines(Fig.2-G,ll),that are most prominent next to aperture but be-come fainter in direction of apex.But longitudinal lines become thicker near the lateral ridge(Fig.2-G,tll),which may be caused by pressure applied to the shell during diagenes.Ventral side almost flat to very slightly convex,and bears the same ornamentation as the dorsum without a median ridge(Fig.2-C,2-D,tr).The apex is damaged to some extent,but it still can be seen that it is bluntly rounded in form,and no septa are visible. Locality and horizon The first member of the Tuoranggekuduke Formation,Emsian Age,Lower Devonian,Chawukar area,Fuyun County,Altay Prefecture,Xinjiang.